In the past, attempts have been made to utilize dead space under one or more horizontal steps for storage purposes. Examples of drawers to be used for storage and adapted for installation under one or more steps may be found in U.S. Pat. Nos. 676,157 and 2,563,436, directed to a stool and step-ladder, respectively. Drawers of these designs are mounted horizontally under one or more steps and are manually slidable by conventional tongue and groove techniques from either a front or rear access to the step. However, notwithstanding these efforts, a storage drawer unit has not been disclosed which uses dead space under or in an unfinished stairway. Furthermore, a storage drawer unit has not been disclosed which is diagonally extensible from the step by hand and safely self-closing under its own weight. Additionally, a storage drawer unit has not been disclosed which facilitates proper registration of the storage drawer under the step during installation and operation.